View Full Version : Chatter 110/220 question

01-27-2012, 02:10 AM
OK, this one has absolutely nothing to do with Parallax, but maybe someone has an idea where to find the answer, or knows the answer with a reference. I'm working through residential codes, but I'm not holding my breath.

220 and 110VAC single phase... typical residential stuff. For the mains I have two legs of 220VAC into the box, a neutral and a ground. From there it branches to 220V and 110V (one leg of 220) circuits. I got no problem with that. It's called a multiwire branch circuit. I've heard different opinions on this and one of them doesn't make sense. One electrician says yep, the other nay.

Supposedly if you run a double breaker, 12/3 220V circuit for a 220V outlet, thou shalt not feed a 110V outlet off one leg of the same circuit.

Um, isn't that exactly what we're doing off the mains? According to some, if you load 30A off one leg of a 20A double breaker it won't trip <--- see previous question..... Forgive me if I do not wish to test this theory :)

Replace the numbers 110 with 120 and 220 with 240 if you prefer.

01-27-2012, 02:11 AM
I'm still digesting this from the National Electrical Code
but the link for this is http://www.nfpa.org/assets/files/pdf/rop/70-a2010-ropdraft.pdf
if anyone is interested.

Loopy Byteloose
01-27-2012, 06:16 AM
110VAC legs should have their own separate circuit breakers as the double breaker for 220VAC is intended to trigger a bit differently (both legs at the same time).

I suspect one electrician gave you a good answer, the other felt that it is none of your business and should hire an electrician to solve such problems.

Reading the code is NOT a training manual - very rough going. Try looking into military and Department of Agriculture manuals at the USA Government Priniting Office for better advice.



The first Google entry is a training manual for Hawaii electrical utility workers. Since it must follow national code, it may be easier reading.

01-27-2012, 08:24 AM
Ok, since this topic is right up alley and a electrician with over 23yrs in the electrical field and now doing maintenance for 10yrs now. This should be easy for me to answer for you.

If you have a 220 vac circuit it should be cennected to a double breaker only in your panel and go directly to the 220 vac devices you need to operate. You shouldn't be tapping off 120 vac from this circuit to use this as another circuit. It's no no, not to code and very safe.

If, you need another 120 vac in that general area you can do the following:
1) Come off another 120 vac circuit in that general area.
2) Run another circuit from your panel based. This means you need to know how much current you will need for what you need to run. Remember that 14 AWG is good for 15 amps and should be connected to a 15 amp circuit breaker and 12 AWG is good for 20 amp circuit and connected to a 20 amp circuit breaker.

If, you need two separate 120 vac circuits. You can use 12/3 or 14/3 ( use the one based on highest current draw of the highest circuit) and connect the black wire to one breaker, the red wire to another breaker and on the other end connect your two separate 12/2 or 14/2 in a junction box by connecting the one 12/2 or 14/2 black wire to black on the 12/3 or 14/2 and other 12/2 or 14/2 black to the red 12/3 or 14/3, which this will leave you the whites which get connected all to together and the grounds get connected all to together.

Home Depot,Lowes or the library should have basic home wiring books which have this information in them, that I just went over.

01-27-2012, 10:26 AM

For the mains I have two legs of 220VAC into the box, a neutral and a ground.

Please allow me to correct you, for residential wiring, in a single phase panel, there are two legs of 120V, a neutral, and an equipment ground.

I don't have an NEC edition in front of me, because my copies were stolen, so I cannot recite the proper codes for you. However, the NEC states that the load must be balanced, and I am sure your question applies to this.

In a 240V/20A circuit, 12-3 w/G as you implied, supplying the necessary power for a 240V outlet, you do not want to tap into this circuit, because it will unbalance the load going back to the panel. This outlet is intended to supply 20A to any given appliance. By tapping into this circuit, you could be robbing amperage needed for the appliance, or not providing enough amperage to any devices you plug into the tap.

The load must be distributed equally between both of the 120V bus bars in the panel.


EDIT: Pertaining to this section of the NEC, I believe there are "exceptions" (special circumstances where it would be permitted). And I believe the exception is for cooktops and ranges only, but I could be wrong about this.

01-27-2012, 01:21 PM
idbruce, I stand corrected, I suppose what I used is called a misnomer. It's two legs of 110/120V out of phase commonly referred to, at least among the general redneck population as two legs of 220.

To all:
I read for quite some time about this last night and I should err of the side of caution right? And I will, but the reason for all this is dumb. From my reading there are two schools of thought. There are a huge number of electricians that want to see this changed, do not think it's a good idea etc. My argument is: Off the main breaker the loads on either hot line will NEVER be balanced, certainly not for a intermittent periods and not for extended lengths of time. It's exactly the same thing. Anyways, the elctrical code as I read it (being the first time reading it and I generally have poor comprehension of twisted legal and code texts such as this) allows such a circuit. There were many entries in the code covering this type of circuit, I could see none that forbid it. I admit I could have interpreted it the way I wanted it to read as well, but I tried to understand and be objective.

Thank you all for the input. This is for my shop by the way. Two separate circuits will cost an additional $75 for the 12/2 110V outlet. It's an extended location so I hated to run the extra cable when technically it was right there in the 10/3.

01-27-2012, 01:29 PM
Without a code book handy, I really can't argue any facts. But just so you know, I also have been an electrician for many years, with most of those years spent in the residentiial field. I would never do it.

Loopy Byteloose
01-27-2012, 03:28 PM
I wouldn't get to heavy into the balanced load debate as the load balance in this set up in never predictable.

What you really should want is safety, reliability, and preservation of home value. I couldn't seem to find anything handy for the USA, but that Manitoba utility DIY guide is excellent.

There are essentially three kinds of circuitry in a home layout: dedicated devices (refrigerator, stove, a/c, and so on); lighting, and outlets. Usually outlets are kept off of lighting so that when you have a fuse blow, you are not in the dark.

Amperage is directly related to wire size; so more amps requires bigger wire. The circuit breaker's rating determines what size the wire should be.

BTW, load balancing is really for industrial consumers that are sucking huge amounts out of the grid; not dinky homes with 120amp service or less. The Grid goes up into tens of thousands of volts and there a balance failure is catastropic.

If you have an outlet that is rarely used and NOT special, you can just connect another wire of the same size to its circuit breaker and share. If you don't and you have space in your box, you can just add new circuit breakers.

IN GENERAL, rural utility companies are far more helpful in DIY wiring according to code as their clients don't have much money. Talking to an electrical inspector in a big city is hazardous to your brain - lots of curve balls.

There are a few never, never items - like don't put your circuit breaker box behind the kitchen stove. When your french fries are on fire, nobody can power down the house.

01-27-2012, 03:33 PM
Captain obvious wants to know why you wouldn't just put a small load center in the shop?
Murray sells a nice little 4 space, 8 circuit indoor box for about $15 bucks, and an outdoor one for $20...

What exactly are you trying to run in your shop? or how many amps are you planning?
How far away are the breakers you are using now? or how long of a wire run are you planning?


01-27-2012, 06:18 PM

Putting a small load center in the center of the shop would cost him more than the now accepted $75 which is already dipping into the Friday Night funds :)


EDIT: Just look at the squirrel avatar holding onto his cache :)

01-27-2012, 06:42 PM
@Loopy Byteloose

The circuit breaker's rating determines what size the wire should be.

This statement is only partially true.

The ampacity of a load determines the circuit size or breaker necessary, and the load should only use 80% of the total amperage capable of being supplied by the over-current protection device. The type and size of wire being utilized determines it's ability to supply the load. And the NEC, for structures contained within the USA, specifies the wire size and type based on the ampacity of the circuit.


Phil Pilgrim (PhiPi)
01-27-2012, 07:00 PM
Not to stir the pot, but there is such a thing as a 120/240 outlet. It's used for things like electric dryers that require 240 for the heating element and 120 for the motor. It takes a four prong plug: 2 hot, 1 neutral, 1 ground. Obviously, with the motor running, the load will not be balanced. But does that really matter? After all, it's almost never balanced at the breaker box either. Otherwise, the power company wouldn't have to run three wires from the pole. (And heaven help your 120V appliances if the neutral wire breaks, leaving the other two intact.)


01-27-2012, 07:14 PM

And heaven help your 120V appliances if the neutral wire breaks, leaving the other two intact.

This is particularly true when pulling circuits from the panel and sharing a common neutral. I can only imagine just how many tvs and computers have been destroyed because of an unsuspecting electrician pulling off a wire nut to a neutral splice in a junction box. Nothing like 240V to release a lot of magic smoke. :)


01-27-2012, 07:41 PM

In fact, just a few weeks ago, I was performing some electrical work for a friend that had another friend do some wiring for him. He disconnected a shared spliced neutral going to two branch circuits. The furnace, two complete bedrooms, and a partial bedroom all had 240V available :)

It was really wierd how this affected the switches for lighting in these areas :)

If you had the right combination of switches (from different areas) in the on or off position, the light would go on. You had to walk to one bedroom to turn on the light in another. :) It was the first time I had ever noticed how this situation affects switching.


01-27-2012, 08:03 PM
I called it a load center, I prolly should have said sub panel instead...:)
I thought that 10/3 was allready pulled to the shop?
what is the 10/3 hooked to? an outlet for a cordless drill charger? and you bring a flashlight, or..
an outlet for the 220 table saw with feeder, shop vac, and the lights?


01-27-2012, 08:06 PM

I also stand corrected:

I called it a load center, I prolly should have said sub panel instead...:smile:

I am surprised I did not catch that in the first place, and then I made the same mistake :)

01-27-2012, 09:12 PM
WHOA! Y'all have given me a lot of information. OK, I should have explained everything up front it seems, but I didn't want to post a two page question.

I have a armored 12/2 circuit, 15A breaker for six 15A 110V outlets in the area. I do not want to tie into this circuit as I'm dedicating these to lab stuff, DC supply, Oscope, etc.
I have a dedicated armored 12/2 15A breaker for four 2x4 T8 lights

the armored 10/3 is what I plan to install on a 30A breaker pair. It's oversized for 30A 220V service new oulets for a welder, abrasive saw OR (not and) a cnc when it takes the place of the welder and saw which will move elsewhere to a new circuit close to the panel.
I wish to install four new 110V 15A outlets in the same area as the four new 220V 30A outlets. I said to myself, "Self, instead of spending $75 for more 12/2 armored cable, why don't you share one hot leg and a neutral from the 10/3 220V 30A circuit you are going to install and place your four 110V 15A outlets right next to each of the four 220V 30A outlets?" then I said, "Hey, that's a great idea! what I genius you are self"

I researched it, found conflicting ideas, posted here cause there's a lot of intelligent people here that know a lot of different things.

What Friday night fund?
Another box isn't a bad idea. I didn't think of that exactly. Run my 10/3 into a box and split into 10/3 for 220 and breakered 12/2 for 110.
Anyhoo, once I figger out what to do I'll save as long as it takes for the parts and do it. Just not real sure what that is just yet :) I'm a little overwhelmed HA!

Phil: I would also like to mention dryers, 110 and 220V supply
220V to 110V plug adapters can be purchased. I'm not really saying that's OK, just that they're available.

01-27-2012, 09:26 PM

You cannot or should not take a 10/3 into a main lug panel and then branch it off to both a 30A double pole breaker and a 15 or 20A single pole breaker. This is definitely not in accordance with the NEC. You are essentially attempting to do the same thing but in a different manner. From the main panel, pull 6/3 to a main lug sub-panel for 50A supply and then branch out from the 30A double pole breaker with 10/3 and from the 15 or 20A single pole breaker with 12/2 or 14/2.


01-27-2012, 10:31 PM

Just for the record, when you first open the NEC, one of the first things you see is a statement of it's purpose, and contained within this statement is the mention of protecting life and property. When you perform wiring methods in direct contradiction with the NEC, you are putting life and property at risk. The NFPA does not just arbitrarily make rules and regulations, they make these rules because life and/or property has been lost.


01-27-2012, 10:55 PM
Alright, I was thinking about things on the way home and aside from everything else, it's not a good idea to pull two lines on a 30A breaker to feed a 15A outlet. If I overload the 15A outlet, the breaker won't trip until things get really toast. So everthing else aside, that itself ruins my idea. I'd need a 15A breaker after the split.

The sub panel would work ignoring the balanced load stuff, but if I'm going to spend money on that, I might as well buy the wire.

Thank you all for keeping me straight!

01-28-2012, 12:07 AM
From the main panel, pull 6/3 to a main lug sub-panel for 50A supply and then branch out from the 30A double pole breaker with 10/3 and from the 15 or 20A single pole breaker with 12/2 or 14/2.
I assumed these instructions when I mentioned installing a new box...:innocent:

Do try to use the thickest wire you can buy, use at least #8 if you can't buy #6 or #4.
It really depends on the length of the run of wire.

Do not use a thinner wire in the middle of two thicker wires like #6--#10--#6, this is bad...:)
Unless of course, you want a resistor...


Phil Pilgrim (PhiPi)
01-28-2012, 12:46 AM
Also, if you use aluminum wire between your main panel and sub-panel, be sure to treat the ends with anti-corrosive grease before clamping them in. It doesn't hurt to work the grease in with a wire brush. Otherwise, you risk eventual overheating and a possible fire hazard.


01-28-2012, 12:52 AM
And since we are discussing the subject of adding a subpanel, within the subpanel, keep the equipment ground seperate from the neutrals (purchase a seperate ground bar), and do not bond the neutrals to the cabinet, leave the neutrals floating.


EDIT: And while you are at it, ensure that the neutral bar is bonded to the equipment ground within the main panel. An unbonded neutral within the main panel can cause magnetic fields throughout the house.

01-28-2012, 01:03 AM
And since you will already be performing electric work, take a moment to inspect the cold water ground and ground rod assembly to ensure that it exists and is intact. And ALWAYS maintain grounding integrity throughout your electrical system.


Peter KG6LSE
01-28-2012, 02:31 AM
what is possible and what is SAFE and what is legal are not allwas the same thing

Form a Pure EE theory point It is doable .. but its risky and not Realy legal ..

01-28-2012, 12:18 PM
Actually the National Electrical Code (NEC) rules are of a "fault tolerant safety" design. This has come about through recording many years of electrocutions and fires, then changing rules and redesigning things so these accidents do not happen again - IF you install everything to NEC rules!

The NEC knows things most people do not know. That is high amperage connections WILL come loose, especially if you are the type to not follow rules and do not torque the connections per the installation instructions for each load center/device.

And when you lose a neutral connection, VERY dangerous things can happen! And again especially for those who do not follow the rules and would not have a proper grounding system.

And ground wires run outside homes/buildings WILL be cut by a lawnmower, become disconnected, or no longer work because someone replaced metal water pipe with plastic! (Then no one will fix these.)

So with that said, you are safest to get an electrical permit before doing home/building electrical work, follow NEC rules, and then have your work checked by the electrical inspector (for safety).

And if your electrical wiring is safe, then no need to worry about having it inspected as it will easily pass with flying colors, right?

The "NEC Handbook" has the rules and pictures/diagrams...

For electrical permits in the U.S., call your local City or County government office and ask where you get these. You can ask them questions. They prefer you do so BEFORE doing any work, then you don't go out and buy the wrong things.

FYI - Multi-Wire Branch Circuits are also called MWBC. To learn more about these, google the following terms...

Multi Wire Branch Circuit

In homes these are common for the garbage disposal / dishwasher outlet.

01-28-2012, 12:26 PM
For electrical permits in the U.S., call your local City or County government office and ask where you get these. You can ask them questions. They prefer you do so BEFORE doing any work, then you don't go out and buy the wrong things.

Some municipalities will even require that you take an electrical test before allowing you to perform electrical work on your own home :)

Loopy Byteloose
01-28-2012, 02:47 PM
SAFE is always power off the circuit before adding on it. If you don't know where to or how to, you shouldn't be doing anything. And of course, SAFE is doing it to code, even if you don't have the permit.

The permit process varies hugely by location. The State of Oregon allows (or used to allow) the home owner to wire their own home (and to plumb it as well), but a licenced electrician had to bring in the service hook up. In big cities in California, you either have to sneek it in or hire and electrician. Every utility and every state has different policy.

BTW, an arc welder and digital computers in the same building with nearby circuits are likely to make a lot of problems. I worked for a plumbing contractor as an accountant that downed all his bookkeeping with a TIG welder. This is far more ambitious than adding one outlet somewhere or setting up a table saw.

01-29-2012, 12:47 AM
Now I feel obligated to mention "Thou shalt not strip the insulation from the wire with ones teeth and/or fingernails.."


Phil Pilgrim (PhiPi)
01-29-2012, 12:51 AM
At least, if you did, you wouldn't nick the wire, which may be the bigger sin. :)


01-29-2012, 01:07 AM
Now I feel obligated to mention "Thou shalt not strip the insulation from the wire with ones teeth and/or fingernails.."

He He! I have a built in wire stripper with my two front teeth. Although I've only used it for small electronic gauge wire. I've never tried it with 120V electrical 12 or 14 gauge wire or lamp cord - and would rather not try.

01-29-2012, 01:08 AM
Nay sir, there be no measure of sin..ALL sin is equal in the eyes of the all powerfull NEC book of knowledge..

LOL, I saw it happen once, a dumb carpenter trying to change a cord end..
He bit down and somehow managed to jerk the wire out of his mouth, funny stuff...
Oh did I mention the cord was still plugged in?.


01-29-2012, 01:24 AM
And was that more than the 9V battery on the tongue reaction?

01-29-2012, 01:31 AM
Oh yah! he danced around for a minute, groaning and mumbling thru his hands holding his mouth...
My brother and I took a second to figure out what the guy had just done, he was in mid sentence.. funny stuff.

Phil Pilgrim (PhiPi)
01-29-2012, 01:36 AM
I cracked a front tooth once by pulling the insulation off of some 30 ga. wirewrap wire. I didn't mention to my dentist what I had done to cause it, since he had already accused me of cracking crab with one of my back teeth. In his words, "Never use your teeth as tools!" Still, though, as occupational hazards go, we have it pretty easy. :)


01-29-2012, 09:16 AM
"Never use your teeth as tools!"

Out of all the advice given within this thread, I think this is the best advice :)

Phil, you say the funniest things. You always get a laugh out of me.

01-29-2012, 02:33 PM
I think there is one exception to the "don't use your teeth" rule..
When you have a fist full of wire that you want to tape together, and you can't set them down or they will scatter,
and the business end of the electrical tape is stuck tight to the roll, You have one free hand, what will you do?
What will you do?...


01-29-2012, 03:09 PM
Hmmmm.... Let me think for a moment....

Reach for my linemans pliers :)

01-29-2012, 03:40 PM
So now I have a fist full of wires in one hand, and pliers in the other...? :blank:

01-29-2012, 08:55 PM
[QUOTE=idbruce;1069852. An unbonded neutral within the main panel can cause magnetic fields throughout the house.[/QUOTE]



01-29-2012, 09:53 PM

This does not dicuss the exact specific point, but it scratches the surface.



EDIT: Also look at the content under Ring Wiring